The study on phage-host interactions and their influence on toxinogeny in C. diphtheriae will be continued. An effort will be made to further test the hypothesis that the tox gene which is present on the phage genome originated as a gene in the host bacterial strain. This will be done by attempting to localize the genes controlling repression of toxin formation in the area immediately adjacent to the prophage insertion site. Parellel to this study a search for a recombination system in C. diphtheriae will be initiated since some system for studying the location of genes in the bacterial genome is essential to studying the interaction of the bacterial phage genomes. Studies on the possible influence of a variety of factors on toxin production are continuing in an effort to identify the regulatory factors involved in the synthesis of toxin. Finally, a group of corynephage mutants with an unusual alteration in their immune pattern will be studied with a view to identifying the basis of this alteration. BIBLIOGRAPHIC REFERENCES: Laird, W. and N. Groman (1976) Prophage map of converting corynebacteriophage beta. J. Virol. 19:208-219. Laird, W. and N. Groman (1976) Isolation and characterization of tox mutants of corynebacteriophage beta. J. Virol. 19:220-227.